Hive swallows NPE if no delegation token found

In case if there is no delegation token put into token file, this line will cause a NullPointerException which is not handled and the user is not notified in any way.

To cause NPE the use case is to have an Oozie Sqoop import to Hive in a kerberized cluster. Oozie puts the delegation token into the token file with id: HIVE_DELEGATION_TOKEN_hiveserver2ClientToken. So with id hive it is not working. However, fallback code uses the key which Oozie provides this way.

I suggest to have warning message to user that key with id hive cannot be used and falling back to get delegation token from the session.

I am creating the patch.